CN116568631A

CN116568631A - Monolithic nanopillar structure

Info

Publication number: CN116568631A
Application number: CN202180072779.6A
Authority: CN
Inventors: 纳吉布·阿什拉夫·克哈利德; 黎惠平; 亚历山大·诺维科夫
Original assignee: 4233999 Canada Inc
Current assignee: 4233999 Canada Inc
Priority date: 2020-08-31
Filing date: 2021-08-16
Publication date: 2023-08-08
Also published as: KR20230056050A; US11094846B1; WO2022040780A1; JP2023538769A; US11393952B1; US20220069163A1; EP4205186A1

Abstract

Gallium nitride (GaN) nanopillar arrays have quantum wells on polar c-faces or semi-polar faces to emit light directed to the ends of the nanopillars, and gap fill materials to direct light emitted in the nanopillars from one end of the nanopillars to an outlet.

Description

Monolithic nanopillar structure

Technical Field

The present application relates to display technology and lighting devices using active semiconductor emitters.

Background

Display technology is undergoing rapid development and evolution. While difficulties remain, miniature light emitting diodes (miniature LEDs) are being used for emerging future generation displays. The color spectrum only partially covers the CIE color gamut while the throughput of assembly using mass transfer methods remains a significant challenge.

The field of display technology currently uses LED backlit Liquid Crystal Shutters (LCDs) to form images for human visual sensing. Organic Light Emitting Diodes (OLEDs) are also being applied to newer products. Current technology is expanding using miniature light emitting diodes (micro LEDs) but still has significant challenges. These challenges are the limited visual spectrum and serious difficulties of assembly of the display. The assembly of displays using micro LEDs requires a new technique called mass transfer, which automatically positions millions of micro LEDs to form pixels with very high precision, and then forms the display. All this is done at very high speeds, making the display cost-effective. This has not been achieved so far.

Review of the journal of science and patents reveals some effort in fabricating light emitters with nanostructures, also known as Nanowires (NWs) and Nanopillars (NC).

The most promising feature of NC emitters is that it has been found that the wavelength of the emission depends on the diameter of the NC without requiring a change of material. For LED materials, different colors require a change in material, so that displays with different colors require assembly of elements from different substrates, i.e. one substrate for each color of the LED. The complexity of such an assembly is a problem. The same semiconductor substrate can provide pixels of different colors using NC techniques. NC technology is also expected to provide illumination sources that may be monochromatic or polychromatic.

U.S. patent publication 2003/0168964 describes light emitting nanowires with organic active regions that fill the void regions within the nanowires and form p-type contacts. The application does not describe how a display is formed with light emitting nanowires, nor any description about Quantum Well (QW) structure and crystallographic axis orientation. Furthermore, the application shows a limited wavelength range on the same wafer. The present disclosure is limited to blue light only.

Us patent 10,177,195 and us patent publication 2019/013345 show the use of nanowires formed using Metal Organic Chemical Vapor Deposition (MOCVD) to fabricate a display. The color produced by the nanowire or group of nanowires is controlled by varying the diameter of the nanowire. This application shows that different materials are used for the active area, requiring different sets of colours to be manufactured on different wafers, which are then lifted and mounted on the back plate. This requires a level of mass transfer technology, but this level has not been reached. These applications do not disclose the formation of electrical contacts.

Us patent 10,263,149 discloses the use of MOCVD and catalyst-assisted epitaxial growth of nanowires. This patent does not describe measures to control the diameter of the nanowires, and thus does not describe controlling the color of light emitted by the nanowires. This application does not describe how a display is formed with nanowires.

U.S. patent publication 2017/0279017 describes the fabrication of nanowires, but does not describe integrated monolithic pixels of different colors arranged on the same wafer. Furthermore, this application combines phosphor technology with nanowires, similar to the way blue LEDs use phosphor for white light.

Us patent publication 2018/0374988 describes a method of fabricating nanowires using InGaN for the active region. The diameter of the nanowires produced determines the color. Electron beam lithography is used to control the diameter of the nanowires being fabricated. This application describes how individual nanowires are electrically driven. This application does not disclose how a display is formed from nanowires, as it only considers a single nanowire.

Ahmed (US 2019/036306), hugon (US 2017/0352601 A1), lu (US 2012/0261686) and Wang (US 2012/0253982) all use MOCVD to grow nanowires and core-shell structures for QWs.

The Ahmed application shows how the wavelength of the emitter can be varied by changing the diameter. Two different colors are shown, but no mention is made of External Quantum Efficiency (EQE) or color gamut that can be covered.

All publications use MOCVD for nanowire growth, growing QWs in a core-shell structure, which means that QWs grow on the m-plane.

The efficiency of NC-based displays is defined by how much current can be converted into light output in the direction of the viewer. When QW grows on the m-plane of NC, light emission is directed to the sides of NC. Even when EQE is good, the light output through the end of NC is hindered by the emission direction.

Only two publications of Zetian Mi and one paper by sekigchi in journal 231104 of applied physics communications (Applied Physics Letters) (2010) show nanowires grown by Molecular Beam Epitaxy (MBE), and only Zetian Mi show QWs grown in nanowires and at least three different wavelengths on a single wafer in a single process. However, zetian Mi does not disclose how a display can be manufactured. These QWs are on the c-plane and the larger diameter nanowires are in the half-pole face. The C-plane emission is expected to have better efficiency of light output through the NC.

Zetian Mi et al disclose emitters on wafers of different wavelengths, the wavelength range being limited to 460nm to 635nm. This amplitude of variation is achieved by varying the diameter of the nanowires. This publication does not limit how the emitted light exits and functions. Measures for providing an electrical connection are disclosed. Therefore, EQE will be limited. Sekigchi et al describe a similar wavelength range of the emitter, but no structure for enhancing the EQE of the device. Electroluminescent (EL) characteristics are not disclosed.

The above summary of the prior art shows that nanowires may have the potential to overcome some or all of the disadvantages in current display technology. However, it is also apparent that none of the prior publications have tried to show how nanowire emitters could be adapted to be arranged into sub-pixels/pixels and to make a complete working display with sufficient emitter efficiency and color quality. Taken together, these publications provide descriptions of nanowire-based emitters that grow different wavelengths on the same wafer and in the same process. Apart from zeian Mi, no growth conditions and how the wavelength changes occur are disclosed.

Furthermore, none of the prior art addresses the problems associated with the change in optical efficiency of light emission with the crystal plane in which the QW grows on GaN crystals.

Disclosure of Invention

Applicants have found that using a nanopillar structure derived from quantum wells grown on the c-plane and semi-polar plane, and a double layer p-type contact structure, provides enhanced light emission levels and uniformity, making it possible to construct a display using this technique. As described in detail herein, the nanopillar structures found in the prior art may not be suitable for building displays because they generally do not produce sufficient intensity, luminosity, contrast, resolution, and the like. The displays described herein using nanopillars overcome the disadvantages of displays using prior art nanopillars.

The gallium nitride (GaN) nanopillar array may have quantum wells on a polar c-plane or a semi-polar plane to emit light directed to ends of the nanopillars, and a gap-filling material arranged to direct light emitted in the nanopillars from one end of the nanopillars to an outlet. The sides of the nanopillars may be coated with a material to reflect light along the longitudinal axis of the nanopillars. The p-doped end of the nanopillar may be metallized and provided with reflective contacts to direct light out through the n-doped end.

In some embodiments, there is provided a nanopillar device comprising: a gallium nitride (GaN) nanopillar array having a negatively doped first end and a positively doped second end with a light emitting region therebetween, the GaN nanopillar array having a gap filler material, wherein light emitted from the light emitting region is directed in the nanopillar to the first end and the second end; a common transparent contact covering a first end of the GaN nanopillar array and providing an exit window for light; a metal coating on the second end of the array of GaN nanopillars, the metal coating having a thickness sufficient to bond with the second end of the array of GaN nanopillars while being thin enough to have low absorption of light emitted from the light emitting region; an array of reflective conductive contacts, each reflective conductive contact covering a metal coating of a number of GaN nanopillars representing a pixel or sub-pixel (sub-pixel) for reflecting light to the exit window, wherein the metal coating provides a reduced resistance between the positively doped GaN of the nanopillars and the reflective conductive contacts; and a driver semiconductor substrate having surface contacts connected to the reflective conductive contact array.

In other embodiments, a nanopillar device comprising an array of gallium nitride (GaN) nanopillars is provided. Each GaN nanopillar comprises the following vertical arrangement: a negatively doped first end region extending the full width of the nanopillar; a second end region of the positive doping, the second end region extending the full width of the nanopillar; a light emitting region grown on one of the c-plane and the half-pole face between the first end region and the second end region; an insulating material layer contacting and covering the sidewall surface over the entire length of each GaN nanopillar, the entire length extending over the first end, the second end, and the light emitting region; and a layer of reflective material in contact with and covering the layer of insulating material to help direct light in the nanopillars to the exit window. The GaN nanopillar array comprises a gap fill material, wherein light emitted from the light emitting region is directed in the nanopillar to the first end region and the second end region. The common transparent contact may cover a first end of the GaN nanopillar array and provide an exit window for light. A metal coating may be on the second end of the GaN nanopillar array, the metal coating being bonded to the second end of the GaN nanopillar array and allowing transmission of light emitted from the light emitting region. The array of reflective conductive contacts may each cover a metal coating of several GaN nano-pillars representing pixels or sub-pixels for reflecting light to the exit window, wherein the metal coating provides a reduced resistance between the positively doped GaN of the nano-pillars and the reflective conductive contacts. The driver semiconductor substrate may have surface contacts connected to the reflective conductive contact array.

The common transparent contact may have a negatively doped GaN layer covering a first end of the GaN nanopillar array. The GaN nanopillar array may be coated with an insulating material, and the insulating material may be coated with a reflective material to help direct light in the nanopillars to the exit window. The gap filling material may include a light absorbing material.

The GaN nanopillar array may include sub-pixel groups having different width dimensions and emitting different colors of light. The light emitting region of the nanopillar may be in a polar c-plane or a semi-polar plane to emit light directed to the first and second ends.

The metal coating may include nickel and gold, which are treated Jing Re to bond with the second ends of the GaN nanopillar array. The metal coating may be about 6nm thick and may contain about equal amounts of nickel and gold.

The array of reflective conductive contacts may be arranged as an array of pixels and the driver semiconductor substrate may be configured to provide an image display device. An array of gallium nitride (GaN) nanopillars may be arranged in a subpixel group for providing a color image display device. The number of sub-pixel groups may be four or more.

The array of reflective conductive contacts may be arranged to drive groups of gallium nitride (GaN) nanopillar arrays to provide different colors, and the driver semiconductor substrate may be configured to provide different voltages to the groups for providing a variable color lighting device.

In some embodiments, a method of fabricating a monolithic nanopillar light emitting device is provided, the method comprising: applying a metal coating on the p-doped ends of the array of gallium nitride (GaN) nanopillars, the metal coating having a thickness sufficient to bond with the p-doped ends of the array of GaN nanopillars while being thin enough to have low absorption of light emitted from the light emitting regions of the GaN nanopillars; and applying an array of reflective conductive contacts, each reflective conductive contact covering a metal coating of a number of GaN nanopillars representing a pixel or sub-pixel for reflecting light to the exit window, wherein the metal coating provides a reduced resistance between the p-doped GaN of the nanopillars and the reflective conductive contacts.

In other embodiments, a method of fabricating a monolithic nanopillar light emitting device is provided, the method comprising:

vertically growing an n-doped first end region of each nanopillar of an array of gallium nitride (GaN) nanopillars on a buffer layer of n-doped GaN, the buffer layer being capable of providing a common contact and an exit window;

vertically growing a light emitting region on a first end region of each nanopillar of the array of GaN nanopillars, wherein a width of the light emitting region is equal to a width of the first end region of each GaN nanopillar;

Vertically growing a p-type doped second end region on the light emitting region of each nanopillar of the GaN nanopillar array, wherein the width of the second end region is equal to the width of the first end region and the light emitting region of each nanopillar;

spin-coating gap filling material between each nano-pillar of the GaN nano-pillar array;

polishing a p-type doped second end region of the GaN nanopillar array;

applying a metal coating on the p-doped second end region of the GaN nanopillar array, the metal coating having a thickness sufficient to bond with the p-doped second end region of the GaN nanopillar array while being thin enough to have low absorption of light emitted from the light emitting region of each nanopillar of the GaN nanopillar array; and

an array of reflective conductive contacts is applied, each reflective conductive contact covering a metal coating of a number of GaN nanopillars representing a pixel or sub-pixel for reflecting light to the exit window, wherein the metal coating provides a reduced resistance between the p-doped second end region of the GaN nanopillar array and the reflective conductive contact.

Further, a driver semiconductor substrate having surface contacts may be connected to the reflective conductive contact array. The GaN nanopillar array may be grown on a buffer layer of n-doped GaN that is capable of providing a common contact and exit window. A driver semiconductor substrate having surface contacts may be connected to the reflective conductive contact array.

The GaN nanopillar array may be coated with an insulating material, and the insulating material may be coated with a reflective material to help direct light in the nanopillars to the exit window.

The GaN nanopillar array may be coated with a dielectric reflective material.

The interstitial spaces between the GaN nanopillar arrays may be filled with an interstitial fill material, which may be a light absorbing material.

The GaN nanopillar array may include sub-pixel groups having different width dimensions and emitting different colors of light.

The light emitting region of the nanopillar may be in a polar c-plane or a semi-polar plane to emit light directed to the first and second ends.

The metal coating may include nickel and gold, the nickel being deposited first, the gold being deposited on the nickel and heat treated to bond to the p-doped ends of the GaN nanopillar array. The metal coating may be about 6nm thick and may contain about equal amounts of nickel and gold.

Drawings

The invention will be better understood from the following detailed description of embodiments thereof, with reference to the accompanying drawings, in which:

FIG. 1 is a view of a gallium nitride crystal plane;

FIG. 2 is an exemplary prior art nanopillar in which a majority of light is emitted laterally;

FIG. 3 is an exemplary nanopillar according to the present disclosure;

FIG. 4 is a schematic diagram of an exemplary nanopillar according to the present disclosure, wherein the emitted light is shown;

FIG. 5 is a flowchart showing steps involved in fabricating a monolithic nanopillar emitter panel;

fig. 6 is a graph showing a relationship between a diameter of a nanopillar and a wavelength of light emitted by the nanopillar;

FIG. 7 is a schematic diagram of an exemplary nanopillar according to the present disclosure, showing the structure of two nanopillars and surrounding layers;

fig. 8A to 8H are schematic views of steps of fabricating a nanopillar display device according to the present disclosure;

FIG. 9 is a schematic diagram of an exemplary display including a number of pixels;

FIG. 10 is a schematic diagram of an exemplary display including several pixels, each having three sub-pixels; and

FIG. 11 is a schematic diagram of an exemplary display including several pixels, each having five sub-pixels.

Detailed Description

The present disclosure relates to displays including nanopillars and methods of manufacturing nanopillar-based displays. Such displays may be used in smartphones, wearable devices, micro-displays, graphic displays, televisions, and other devices. For clarity, the term Nanopillar (NC) is used throughout this disclosure.

Basic characteristics of a display

The display is typically a two-dimensional arrangement of pixels, which in turn are made up of sub-pixels. The display may have a single subpixel per pixel or multiple subpixels of one pixel. The pixels are typically arranged in a two-dimensional matrix in which each subpixel has a variable emission level that can be set externally. Important attributes required for a display are resolution, color range (gamut), intensity range (contrast), field of view, and speed at which pixels can be varied. Uniformity of color and intensity is particularly critical when manufacturing useful displays.

Characteristics of the human eye

The manner in which light emitted by a display is perceived by a human observer depends on the characteristics of the human eye. The human eye has three different types of cones, each type being sensitive to different bands of wavelengths known to be centered at certain wavelengths. The exact center of wavelength varies among the human population, but is typically in the following bands: blue is 400 to 500nm, green is 500 to 600nm, and red is 520 to 680nm.

Color perception is also affected by the rod response, which provides a larger dynamic range, but only gray scale perception. The eye perceives colors in a very complex manner, which involves the processing of colors by the human brain. Most wavelengths of light activate various types of cones, as is well known in the art. The only exceptions are wavelengths below about 415nm (which only activate the blue cone) and wavelengths above about 680nm (which only activate the red cone). The entire possible color range is created by the ratio of the information and the different intensities available to the brain from the three cones (red, green and blue) in the human eye. However, current semiconductor technology cannot produce the correct green color.

The blue cones are the most sensitive, but only account for 2% of all cones, the green cones account for 65% of all cones, and the red cones account for the remaining about 33% of all cones. These three types of cones have different responses to the same level of intensity/luminosity of light. In other words, light of a given luminosity will induce a different response from the collective green, red, and blue cones in the eye. As can be appreciated, the brain perceives red when there is some stimulation of the red cone and no stimulation of the green cone. The different amounts of stimulation of the cones enable the visual cortex to perceive the wavelength of light (i.e., its color). The visual cortex also receives signals from rods in the retina that provide additional brightness information.

Table 1 below shows the relative response of cones compared to the response of green cones. As shown in table 1, the luminosity of the three light sources is the inverse of the sensitivity. Thus, if the luminosity of green is 1mW, then the luminosity of red will be 1.33mW and the luminosity of blue will be 3.85mW.

Viewing cone	Relative response	Green = 1mW light source required luminosity
			Blue color	0.26	3.85mW
Red color	0.75	1.33mW
			Green colour	1	1.0W

Table 1: the power per RGB emitter required to match full spectrum to white light

In a display, light may be emitted in a pixel, as described above. Each pixel may include one or more sub-pixels, and each sub-pixel may emit light at a particular wavelength. The light emitted by the sub-pixels may be used together to activate red, green and/or blue cones in the eye to varying degrees. Typically, the visible light acts additively such that the intensity of the first subpixel adds to the intensity of the second subpixel. The brain may then process the activation of the entire cone to produce a perceived color. The present disclosure combines the characteristics of the eye described above with the characteristics of the nanopillars to design and fabricate a display.

Gallium nitride crystal face

Gallium nitride (GaN), a group III-V compound semiconductor, is a wurtzite (hexagonal) crystal. The crystal has a face as shown in fig. 1. The m-plane is parallel to the vertical axis, the c-plane is orthogonal to the vertical axis, and the semi-polar plane is tilted from one side of the crystal to the opposite side as shown. As known in the art and described in detail herein, the different axes of the crystal have different electrical characteristics that affect the quantum efficiency of the QW grown thereon.

Prior art-core-shell quantum well (m-plane)

As described herein, the only way that light emitted from the nanopillars can be used for display and illumination applications is when the equivalent Quantum Wells (QWs) are grown on the c-plane and semi-polar plane; rather than on the m-plane. As is well known in the art, metal Organic Chemical Vapor Deposition (MOCVD) processes can grow QWs on m-planes only. Thus, all prior art techniques using MOCVD processes may not bring satisfactory results for display applications. The most important limitation of MOCVD grown QW as a core-shell structure is that a large portion of the light is orthogonal to the longitudinal axis of the nanopillar. Fig. 2 shows such a prior art nanopillar grown on the m-plane, and for such a nanopillar, light is absorbed or reflected by an adjacent nanopillar.

In fig. 2, the p-type contact 51 is generally opaque and thus further reduces light that may be transmitted on the axis of the nanopillar. Furthermore, because they are grown on the m-plane, QW 57 may emit light with a limited angular distribution on each side of each nanopillar only. Growing QW on GaN using an MOCVD process will naturally produce a core-shell structure as shown in fig. 2. Currently, when QW is grown on GaN using an MOCVD process, growth is not currently available on faces other than the m-face.

In such prior art embodiments, a majority of the light is emitted orthogonally to the vertical axis and is absorbed or reflected from the next nanopillar. Only a very small amount of light will be emitted towards the viewer of the display and the light will be scattered to an extent that may hinder a coherent display of the image. Advantages of MOCVD to grow QWs on the m-plane include having a large QW surface area. However, even with an increased surface area (many times greater than the equivalent QW structure established on the c-plane), little useful light is emitted, meaning that the effective EQE is very low.

Quantum wells on c-plane and semi-polar plane

In prior art references that teach QWs grown on c-plane and semi-polar plane, they do not show that these planes have any advantage over the core-shell, and do not show effective external quantum efficiency (E ² QE) differences. Furthermore, the prior art references do not show how sub-pixels and pixels can be formed to construct a color display.

Molecular Beam Epitaxy (MBE) grows QWs on the c-plane or semi-polar plane allowing light emission to exit vertically along the longitudinal axis of the nanopillar, which, incidentally, is directed towards the viewer. By providing means for enhancing light extractionMost of the light will be useful, giving a very high E ² QE。

Fig. 3 is a schematic diagram of one such nanopillar having QWs grown on the c-plane or semi-polar plane by the MBE process. The natural part of the MBE process is that the QW grown on the c-plane and semi-polar plane depends on the diameter of the nanopillar. For example, QWs may be formed on the m-plane when the diameter (or cross-sectional area) is small, and QWs may be formed on the m-plane when the diameter is large. It is then well understood that the c-plane and semi-polar plane are the only methods of QW growth on the nanopillars and provide a means of forming a display. Referring to fig. 3, the nanopillars may have a buffer layer 59, which may serve as a common electrode (e.g., an n-type GaN layer), and which is on top of the structural substrate 60, which may be necessary in the nanopillar growth process. Each nano-pillar may be grown such that n-type GaN layer 65 is in contact with buffer layer 59. Thereafter, an active region including QW 61 may be grown on top of n-type GaN layer 65. The nano-pillars may also include a p-type GaN layer 63, which may be electrically driven by a separate electrode.

Although fig. 3 shows the nanopillar structure during the production process, fig. 4 provides a more detailed view of the nanopillar structure of the individual nanopillars (i.e., the complete structure without the interpillar filler material) after the production process is completed. Therefore, it can be observed that the growth substrate 60 has been removed, and the buffer layer 59 serving as a common electrode is a layer through which light emission is emitted from the nanopillars. To aid in visualizing the light emission, light rays are shown. Although buffer layer 59 is shown in fig. 4 as being on a single nanopillar, this is a schematic view of a single pillar, and it is understood that an n-doped GaN 59 layer will span all nanopillars.

Since the nanopillar shown in fig. 4 can be used in a display or illumination panel, a back plate 69 comprising the necessary connections to each subpixel and electrical drive circuitry can be connected to a conductive p-type contact layer 67 that can also function as a reflector. Thus, the p-type contact layer 67 may serve as both an electrical connection between the p-type GaN layer 63 and the backplate 69 and as a reflector that reflects light emitted by the QW 61 toward the opposite side from where the viewer is located. Thus, the light transmission may have a significant increase. As described below, layer 67 may be a complex layer that provides good conductive contact with p-type doped GaN, with band gap energy that makes it difficult to establish an electrical connection. This portion of the complex layer may be transmissive (i.e., only slightly absorbing). Although contact layer 67 is shown in fig. 4 as being on a single nanopillar, this is a schematic view of a single nanopillar, and it will be appreciated that this layer 67 will span all nanopillars in a given pixel or subpixel.

As described herein, the diameter of a nanopillar affects the wavelength of photons it emits. Fig. 6 shows a graph of diameter versus wavelength. It can be seen from the graph that the larger the diameter, the smaller the wavelength produced. Since the diameter of the growing nanopillar can be controlled by the MBE process, the color of the emitted light can be controlled. Thus, pixels and sub-pixels with exactly the desired nanopillar distribution can be created for each wavelength.

PREFERRED EMBODIMENTS

A monolithic single process color emissive substrate.

The present disclosure relates to methods of fabricating monolithic light emitters from III-V compound semiconductors using Selective Area Growth (SAG) of the nano-pillars, multiple QWs, and another III-V structure and p-type contact on top as described in detail below. A plurality of these nanopillars may then form a subpixel. One or more of these subpixel groups then form a pixel. For RGB sub-pixels, the number of these sub-pixels is three, but more than three wavelengths can be used using the present technique. The desired wavelength and the number of nanopillars dedicated to each wavelength can also be selected to improve the color gamut and efficiency of the display.

The process begins by providing a process substrate (process substrate), such as a sheet of sapphire or silicon. A buffer layer of negatively doped GaN is deposited on one side of the process substrate. This buffer layer 59 will eventually become the emission window of the display and the common contact for the nanopillars. A 2 μm Mo metal layer may be deposited on the backside of the sapphire (or silicon) substrate for uniform and efficient heat transfer from the heater to the process substrate. A thin Ti layer (10 nm) is first used as a growth mask on buffer layer 59 for selective area epitaxy of the GaN nanopillars. The nano-sized hexagonal holes having a certain lateral dimension "d" arranged in a triangular lattice, e.g. lattice constant "a", may be manufactured, e.g. using electron beam lithography and reactive ion etching. The Ti mask may be nitrided at about 400 ℃ prior to the growth of the nanopillars to prevent cracking and degradation during the growth process. Then, the n-type GaN (500 nm) and p-type GaN (270 nm) nanopillar segments may be grown in an MBE system at substrate temperatures of about 980 ℃ and 960 ℃, respectively, for example, at a nitrogen flow rate of about 0.6sccm and a Ga flux of about 2.5X10-7 Torr. Several pairs of InxGa1-xN (-3 nm)/GaN (-3 nm) can be sandwiched between an n-type GaN segment and a p-type GaN segment as multiple QW active regions. The growth conditions of the active region may include: the substrate temperature is about 735 ℃, the nitrogen flow rate is about 1.2sccm, and the beam fluxes of Ga and In can be 1.8X10-8 Torr and 9.0X10-8 Torr, respectively. Si and Mg may be used as an n-type dopant and a p-type dopant, respectively. Reference herein to substrate temperature refers to thermocouple readings on the backside of the process substrate. The actual substrate surface temperature is estimated to be about-100 to 150 c lower, depending on the dimensions of the substrate and sample. When the nano-pillars have grown to a desired height, the residual Ti mask may be removed by a cleaning process.

Fig. 7 shows the resulting structure of the preferred embodiment as described herein, including the nanopillar interlayer that may be added after the growth of the nanopillars is completed. In this embodiment, the n-type contact may be performed through the buffer layer 59, which may be an n-type GaN layer. A nano-pillar n-type GaN layer 65 is grown on this buffer layer 59, and QW 61 is also grown on top of the n-type GaN layer 65. Then, a p-type GaN layer 63 may be added on top of the active layer 61. The p-type contact recombination layer 67 may provide the necessary electrical connection for the p-type GaN layer while enhancing the emitted light intensity by reflecting light that would not otherwise be emitted from the nanopillars toward the side opposite the exit.

In a preferred embodiment, the p-type contact recombination layer 67 may include several layers, such as a Ni layer 75, an Au layer 73, and a reflective metal layer 71. For light transmission, metallized interface layers 75 and 73 are combined with p-type GaN to allow current to be conducted between the p-type GaN to metal conductor 71. The material thickness of the p-contact interfacial layer is important. The thicker the Ni/Au layer, the greater the absorption and loss of light. The preferred embodiment may use 3nm of each metal for the deposition of the p-type contacts. Other metals for the metallization layer (such as Pd) may also be used. These two metals form a complex in which Ni/Au fuses with p-type GaN at the appropriate temperature. Below a thickness of about 3nm, such fusion with p-type GaN may not occur and Ni/Au may not be able to withstand probing and delamination. However, it may be optimal that these layers remain at about 3nm so that light emitted towards that side of the display (i.e. the opposite side of the exit opening towards the viewer) can pass through and reflect on the reflective and conductive layer 71 added on the Au layer 73. With a total thickness of the Ni/Au layer of about 6nm, the light passing through the layer and returning may have less than about 10% loss (i.e., most of the light emitted toward the reflector is reflected back to the exit of the nanopillar).

There may be several layers between each nanopillar in order to enhance light transmission and ensure electrical insulation so that the nanopillar emitting light may be confined to the desired nanopillar (i.e., controlled by the particular electrode being powered rather than induced by the adjacent nanopillar being powered). Thus, each nano-pillar may be first surrounded by a transparent insulating layer 81. A reflective layer 79 may be added beyond the isolation layer 81 such that the reflective layer 79 may reflect light emitted toward one side of the nanopillar back to the nanopillar. Thus, the reflective layer 79 may increase the light propagating toward the exit of the nanopillar so that more photons may reach the viewer.

The insulating layer 81 may include SiO ₂ And the reflective layer 79 may comprise aluminum (Al) or a suitable dielectric material that is reflective throughout the visible spectrum or at least to the emission wavelength of the nanopillars. Finally, an opaque absorptive inter-nanopillar filler 77 may be added so that there may be no light transmission between the nanopillars or no external light reflected from the interstitial spaces between the nanopillars. The filler material 77 may be polyimide, optionally with the addition of graphite or other pigmentsMaterials to improve light absorption, such as absorption coefficients greater than about 0.8 for white light. Thus, the filler material may have light absorbing properties, including escape from the residual emission of the reflective coating and light incident on the surface from the environment.

Device formation

From a semiconductor-based nanopillar structure to making each nanopillar a device that functions upon application of a current, then enhancing light extraction in a manner suitable for a display, the steps described below may be involved and form part of the preferred embodiment. Those skilled in the art will appreciate that variations may be made to the steps described herein without departing from the teachings of the present disclosure. The different steps of producing the display or illumination source are listed in the flow chart of fig. 5, and fig. 8A to 8H show the monolithic device at a corresponding stage of manufacture.

In step S1, a support substrate is provided. In step S2, a uniform layer of negatively doped GaN is grown on a support substrate. As shown in fig. 8A, a number of nano-pillars are first grown on a buffer layer 59 located on a structural substrate 60. The substrate 60 may be silicon (Si), sapphire, or bulk GaN with a buffer epitaxial layer. A thin layer of mask material may be deposited onto the substrate (step S3), and the substrate etched (step S4) to act as a growth mask for selective area epitaxy of the GaN nanopillars. The mask material may be any hard material, as epitaxial growth may require higher temperatures (e.g., it may be titanium (Ti)).

The nanopillars are grown using the MBE process (step S5), as described herein. A Quantum Well (QW) is grown on the n-type doped GaN nanorods (step S6), and then p-type doped GaN is grown on the QW region to continue the growth of the nanorods (step S7). Once the nanopillars are completed (i.e., the p-type GaN layer is grown), the mask material may be removed and SiO may be used ₂ The passivation layer of (a) coats the nano-pillars (step S9), as shown in fig. 8B. Then, the passivation layer 81 may be coated with a metal reflective layer 79, which may be aluminum (Al) or an electrically insulating dielectric material (step S10). The reflective layer 79 and the passivation layer 81 may be completed by a sputtering process. FIG. 8C shows the following step, in which a light absorbing material 77 may be deposited on the nanopillarsAnd the region above the nanopillar (step S11).

The filler absorbing material 77 may be deposited using any suitable deposition process known in the art, such as by spin coating and firing.

Planarization

As shown in fig. 8D, the wafer is then polished using a chemical mechanical polishing/planarization (CMP) process (step S12) to expose the tops of the nano-pillars. Thereafter, the p-type GaN layer on top of the nanopillars may be used for further processing.

P-type contact

Referring now to fig. 8E, a thin layer of Ni (layer 75, step S13) and then Au (layer 73, step S14) may be deposited on the exposed top of the nanopillars, which may be about 3nm thick. The Ni/Au layer may then be annealed (step S15). As described herein, this forms a p-type contact that is highly transparent to visible light, and the Ni/Au metallic interface layer absorbs less than about 10% of the round trip light. Metal reflective contacts covering the pixels or sub-pixel groups of the nanopillars are deposited, for example by depositing a uniform layer and etching the spaces between the individual contacts (step S16). As shown in fig. 8E, each subpixel can be connected to the same Ni/Au layer 75/73 and metal reflective contact 71 so that the entire subpixel can emit light simultaneously when energized. As described herein, each subpixel is composed of a plurality of nanopillars that emit light at the same or similar wavelengths. This may be desirable because a single nanopillar may not emit enough light to exhibit sufficient characteristics to achieve a normal display (i.e., multiple red nanopillars are required to emit light simultaneously to provide sufficient red light for a single pixel).

The Ni/Au layers 75, 73 may be annealed at 450 ℃ for 10 minutes to produce the desired p-type contact. To complete the device structure and provide current paths for the individual subpixels of the display, a reflective and conductive layer 71 may be deposited for the positive electrode, as shown in FIG. 8F. The p-type contacts of all sub-pixels in the pixel are connected and routed to match the pattern on the silicon backplane 69 to the drive electronics (step S17). The silicon backplane 69 is not part of the present disclosure, but is well known in the art, and in the case of an illumination panel, all sub-pixels may be driven in a similar manner, while in a display, individual pixels are addressed and driven. The reflective and conductive layer 71 may reflect light coming out of the top of the nanopillar back into the nanopillar.

As shown in fig. 8G, the sapphire substrate layer 60 may then be removed from the wafer (e.g., stripped to remove the sapphire layer, step S18). For the negative electrode, the n-type GaN common layer (i.e., buffer layer 59) at the bottom of the emission structure of the nanopillar may thereafter be connected to a common source of electrical power source 85. Those skilled in the art will appreciate that the negative and positive sides of each nanopillar may be reversed, again determined by the alternating design of the silicon back plate and nanopillar.

As shown in fig. 8H, the resulting single piece display, or portion thereof, is now completed, with light being emitted such that it is visible to a user of the display.

While the fabrication process described above involves growing the nanopillars on an n-doped buffer layer, it will be appreciated that one may begin with growing p-doped nanopillars. In this case, the top surface of the n-type doping of the monolithic device will be polished, instead of the top surface of the p-type doping. For a common electrical contact, there will be no n-doped layer across the nanopillar, so a transparent electrode can be deposited on the n-doped side of the device. For a p-doped surface, it will be separated from the support substrate and polished to expose the p-doped end of the nanopillar. The metallization and deposition of contacts will be the same as described above.

Number of nanopillars per subpixel

The number of nanopillars in each subpixel can be determined using the following formula:

N _λx ＝P' _λx /(P _nw ×R _λx )。

wherein N is _λx Is the number of nano-pillars in the subpixel, P' _λx Is the effective power output by the sub-pixel, P _nw Is formed by single nano column at V _fd Maximum power of lower output, and R _λx Is the relative photometry sensitivity (relative photometric sensitivity) of the human eye to the light emitted by the sub-pixels. The display may includeThree sub-pixels configured to emit red, green and blue light, respectively.

In some embodiments, a nanopillar-based display includes: a plurality of pixels, each pixel comprising five sub-pixels, each sub-pixel comprising a plurality of nanopillars, wherein each of the plurality of nanopillars is configured to emit light at a particular wavelength; a back plate connected to all of the nanopillars of the display; a plurality of contacts, each contact connected to a nano-pillar of a single sub-pixel of a single pixel, wherein each of the five sub-pixels includes a different number of nano-pillars. A first subpixel of the five subpixels may emit light at about 700nm, a second subpixel of the five subpixels may emit light at about 610nm, a third subpixel of the five subpixels may emit light at about 565nm, a fourth subpixel of the five subpixels may emit light at about 470nm, and a fifth subpixel of the five subpixels may emit light at about 400 nm. Each of the first subpixel and the fifth subpixel may include more nano-pillars than the second subpixel, the third subpixel, or the fourth subpixel.

The display may include a control system configured to control which of the five sub-pixels in each pixel is activated. The control system may include an ambient brightness sensor configured to detect whether the brightness of the environment surrounding the display is above or below a threshold. The control system may be configured to activate all five subpixels when the brightness is below the threshold and to activate only the second subpixel, the third subpixel, and the fourth subpixel when the brightness is above the threshold.

In some embodiments, a method of fabricating a nanopillar-based display may include determining a number m of subpixels in each pixel of the display, a wavelength λx (subpixels x emit light at wavelength λ), and a maximum operating power P' _λx (subpixel x emits light at wavelength λ at this maximum operating power); confirm the voltage V of the operation of the nanopillar on the display _fd Power P of lower emitted light _nw The method comprises the steps of carrying out a first treatment on the surface of the And the relative photometry sensitivity R of the human eye to light of wavelength λx of each λx _λ The method comprises the steps of carrying out a first treatment on the surface of the Counting the number N of nanopillars in each subpixel _λx Wherein calculating comprises solving the following formula: n (N) _λx ＝P' _λx /(P _nw ×R _λx ) The method comprises the steps of carrying out a first treatment on the surface of the Determining a pattern of nanopillars arranged in pixels, each pixel having m sub-pixels, wherein the pattern provides N for each pixel of each wavelength λx _λx And growing the nano-pillars on the substrate in the determined pattern.

Fig. 9 shows a schematic diagram of a nanopillar-based display 150. As discussed above with respect to fig. 9, display 150 may include a two-dimensional array of pixels 151. Each pixel 151 may include one or more sub-pixels 111a, 111b, 111c. Each subpixel 111a, 111b, 111c may comprise a set of nanopillars that emit light at a desired wavelength λa, λb, λc. The total number of nanopillars in each set may be selected such that the subpixels 111a, 111b, 111c may emit light at a desired maximum brightness. The desired total maximum brightness may be determined by the ambient environment in which the display will be used. The brightness of the pixel is then simply L/T, where L is the total brightness of the display and T is the number of pixels in the display.

Designing the display shown in fig. 9 may entail selecting the values listed below under "given values", determining the characteristics listed below under "known values", and calculating the values listed below under "calculated values". The given value and the known value can be used to calculate N _λ1 、N _λ2 ......N _λm Where m is the number of sub-pixels in each pixel of the display, and N _λx Is the number of nanopillars required to emit light at wavelength x in each subpixel of the display. After determining the number of nanopillars for each subpixel, the size and area of the subpixel can be selected based on the distance between the subpixels (which can affect the contrast of the display).

Exemplary calculations are provided below.

Examples of nanopillar-based display designs

A first exemplary display is shown in fig. 10 and is similar to a standard RGB display except that green is more demanding in terms of CIE color gamut. As described above, each pixel 151 of the display 150 includes a red subpixel 111a, a green subpixel 111b, and a blue subpixel 111c. Thus, the following values may be selected and determined for display 150:

t=1125 pixels 2436 pixels= 2740500 pixels.

L=5000 nit=92 watts

m=3 sub-pixels

λ ₁ =635 nm (Red)

λ ₂ =530 nm (green)

λ ₃ =450 nm (blue)

L _p ＝L/T＝92/2740500＝33.5×10 ^-6 W＝P _p ；

We note here that the luminosity L of each pixel _P Equal to the power output P of each pixel _P In watts. We now consider that the nanopillars operate at a maximum operating point, each different wavelength at a different V _fd And current density. All producing the same amount of power. Thus, the desired power per subpixel is P' _λ1 ＝P' _λ2 ＝P' _λ3 ＝33.5×10 ^-6 /3＝11.1×10 ^-6 A tile.

The power must then be normalized for the different relative responses of the cones of the human eye. R is R ₆₃₅ ＝0.75；R ₅₃₀ ＝1；R ₄₅₀ =0.26. The relative photometry sensitivity of the eye to light of these wavelengths may be based on the characteristics of the human eye discussed above.

Because of P _p ＝P _nwλ1 +P _nwλ2 +P _nwλ3 We obtain P from the measurement results _nwλ1 ＝P _nwλ2 ＝P _nwλ3 ＝1×10 ^-6 W。

Thus, the number of nanopillars required to emit light at each wavelength for each subpixel can be calculated as follows:

N ₆₃₅ ＝(P' ₆₃₅ /(P _nwλ1 ×R ₆₃₅ ))＝(11.1×10 ^-6 /(1×10 ^-6 ×0.75))＝14.8＝15

N ₅₃₀ ＝(P' ₅₃₀ /(P _nwλ2 ×R ₅₃₀ ))＝(11.1×10 ^-6 /(1×10 ^-6 ×1))＝11

N ₄₅₀ ＝(P' ₄₅₀ /(P _nwλ3 ×R ₄₅₀ ))＝(11.1×10 ^-6 /(1×10 ^-6 ×0.26))＝42.7＝43

based on the above calculations, each pixel 151 of display 150 will be designed to include: 15 nanopillars, the 15 nanopillars emitting 635nm light (red light); 11 nanopillars, the 11 nanopillars emitting light at 530nm (green light); and 43 nanopillars, the 43 nanopillars emitting light at 450nm (blue light). Looking at the above calculation, one will notice that at R _λx The greatest change in value occurs. Based on these values, it is not surprising that the display requires the most blue nanopillars and the least green nanopillars. The expanded pixel 151 in fig. 10 generally shows the proportions of red, green, and blue nanopillars based on this calculation.

The display described in this example may be similar to current RGB displays. However, it also presents further advantages over such a display. First, such a display may consume less power because the nanopillars require lower voltages than the micro-LEDs. This may be particularly advantageous for portable devices that rely on battery power, such as smartphones and wearable devices; thus, such a display may extend battery life. Second, such a display may be easier to manufacture than a micro LED display because all the nano-pillars may be grown on a single substrate. This may significantly reduce the cost of the display.

Example two of nanopillar-based display design

A second exemplary display is shown in fig. 11 and provides an enhanced energy efficient five color display. Each pixel 151 of the display 150 may include five sub-pixels 111a, 111b, 111c, 111d, 111e having wavelengths of 635nm, 530nm, 450nm, 570nm, and 420nm, respectively. The first three sub-pixels may emit light at the following wavelengths: these wavelengths may be combined to provide light in a significant portion of the visible spectrum. These sub-pixels will be the same as the sub-pixels in the first example, including the number of nano-pillars they contain.

The remaining two sub-pixels may emit light corresponding to wavelengths of maximum sensitivity of the red and blue cones. At maximum sensitivity, less luminosity is required to produce the same effect in the human eye. This translates into a smaller current and thus reduced power consumption. The number of nanopillars in the two sub-pixels will be smaller due to the higher sensitivity of the viewing cone.

An algorithm may be used to select the intensities of the five sub-pixels to achieve the desired color in the pixel. In some applications, it may not be necessary to use red and blue subpixels whose respective cones have low sensitivity. The red and blue subpixels are not required for the desired color. Higher sensitivity sub-pixels may alternatively be used.

While sufficient nanocubes can be provided for the first wavelength and the third wavelength to provide the same peak brightness for all colors, a complete (or near complete) CIE color gamut display can also be reserved for indoor or head mounted display applications, where lower intensities of the display are acceptable. For smartphones, tablet computers, wearable devices, and graphic displays that need to operate when exposed to sunlight (and in extreme cases, under direct sunlight), greater display brightness is required. Such brightness may preserve other choices for wavelengths for which the viewing cone is more sensitive, thereby saving display power even though such wavelengths do not allow the same full or near full CIE color gamut to be achieved.

It can be understood that when a low-luminance regime and a high-luminance regime are provided, the division of the drive signal power to the sub-pixels varies depending on the regime. In a low brightness regime, all sub-pixels are used to provide the desired pixel color. In a high brightness regime, the violet and dark red sub-pixels are either turned off or used to make a reduced contribution to the brightness of the desired color pixel within a reduced CIE gamut.

To achieve the two different color regimes discussed above, the display may be controlled by a control system. The control system may include an ambient brightness sensor configured to sense the brightness of the screen being viewed. When the brightness sensor senses that the brightness is below a certain threshold, the control system may command the display to use all five subpixels. This command may be performed by supplying voltages to all five sub-pixels. When the luminance sensor senses that the luminance is above the threshold, the control system may command the display to use only three sub-pixels, for example, by providing voltages to only those sub-pixels. In some embodiments, the control system may include a user interface that may allow a user to manually switch between two different regimes.

Those skilled in the art will appreciate that the control system discussed herein may be used in conjunction with various subpixel configurations to provide different color schemes under different ambient lighting. This may allow the display according to the present disclosure to be very efficient while displaying a wide color gamut. Further, such a control system may be used to switch the display between any number of display regimes, and may depend on any environmental sensor.

As discussed above, the display shown in fig. 11 may be very efficient while providing light along nearly the entire visible spectrum. The sub-pixels 111a, 111b, 111c emitting light at 635nm, 530nm and 450nm can be combined to produce any color defined by these principal wavelengths and can be seen in the CIE color space diagram. The sub-pixels 111d and 111e of 570nm and 420nm, respectively, are intended to reduce power consumption, since the color space that can be generated by these sub-pixels will not be as large, but will be very effective in combination with the first three 530nm emitters at the peak sensitivity of the blue and red cones.

Because 530nm, 420nm, and 570nm are near the peaks of the cone activation, very little power and few nanopillars are required to achieve the desired luminosity for the sub-pixels that emit these wavelengths. This can be seen in fig. 11, where fewer nanopillars are required to emit light at these wavelengths. 635nm and 450nm do not meet the activation peaks of the myopia cones, and thus the sub-pixels 111a, 111c emitting light at 635nm and 450nm may require more power and more nanopillars.

In some embodiments, the nanopillar-based display may be processed to improve its contrast. The contrast may be the difference between the highlights and shadows in the image and/or the difference between the luminosity of the light emitted by the display and the background. Contrast can be measured in ratios. The contrast may be limited by the amount of ambient light reflected from the display and any light leaking from the nanopillars into the space between the nanopillars.

The contrast of a nanopillar-based display may be improved by using one or more of the following methods. First, a contrast-enhanced color filter may be placed on the emitter surface. These filters can improve contrast by selecting filter colors that match the colors of the display. For example, for an RGB display using three sub-pixels, a red filter, a blue filter, and a green filter may be selected. These filters may eliminate all ambient light of other colors and absorb a portion of the light transmitted through the filters. Thus, the background may be blackened and the color of the display may appear brighter. Second, a light control film coating (also referred to as an anti-reflective film) may be applied to the front surface of the display. These coatings can absorb ambient light in the region between pixels by absorbing photons emitted from the spaces between the nanopillars. Third, a light polarizer may be used. After passing through the polarizer, the ambient light may be modified and captured by the filter. The pixel light passing through the filter may appear as bright light against a dark background created by ambient light.

By filling the spaces between the nanopillars with a light absorbing material, the background emission of light escaping through the nanopillar walls can be reduced. This may reduce sidewall emission and increase contrast. Such methods may be used to reflect photons emitted from the sidewalls back into the nanopillars, in addition to the methods described elsewhere, which may also contribute to higher contrast.

The fabrication methods and resulting features described above may be applied to nanopillar devices used as displays, such as smart phone displays. They may also be applied to devices manufactured for illumination purposes or as light sources, as well as devices for projecting images onto the retina or may be used on the surface of digital camera viewfinders and micro-displays of virtual/augmented reality head mounted displays, or devices manufactured for other similar purposes. In these devices, the nanopillars are similarly fabricated and create groups for the desired color gamut and intensity. The calculations described herein can also be applied to any type of nanopillar device.

In the case of a lighting device, the color temperature may be adjusted by using two or more colors. The use of more wavelengths may provide illumination that feels more natural, as is the case with natural daylight. If desired, the driver may provide a controllable and variable current to each set of different wavelength nanopillars to change the color temperature, or the device may be designed to provide a fixed wavelength component. When the optical arrangement mixes the light output from the device, it is possible to have groups of nano-pillars of different wavelengths arranged as large blocks or macro-sub-pixels (rather than providing closely staggered sub-pixels), different color blocks will be noted when the device is directly viewed, but these color blocks will be mixed by the optical arrangement, thus presenting a single tone of illumination.

Claims

1. A nanopillar device comprising:

an array of gallium nitride (GaN) nanopillars, wherein each GaN nanopillar comprises:

a negatively doped first end and a positively doped second end with a light emitting region therebetween;

an insulating material layer contacting and covering sidewall surfaces over an entire length of each GaN nanopillar, the entire length extending over the first end, the second end, and the light emitting region; and

a layer of reflective material in contact with and covering the layer of insulating material to help direct light in the nanopillars to an exit window,

and the GaN nanopillar array having a gap fill material, wherein light emitted from the light emitting region is directed in the nanopillar to the first end and the second end;

a common transparent contact covering the first end of the GaN nanopillar array and providing the exit window for the light;

a metal coating on the second end of the GaN nanopillar array, the metal coating having a thickness sufficient to bond with the second end of the GaN nanopillar array while being thin enough to have low absorption of the light emitted from the light emitting region;

An array of reflective conductive contacts, each reflective conductive contact covering the metal coating of a number of the GaN nanopillars representing a pixel or subpixel for reflecting the light to the exit window, wherein the metal coating provides a reduced resistance between the positively doped GaN of the nanopillars and the reflective conductive contacts; and

a driver semiconductor substrate having surface contacts connected to the reflective conductive contact array.

2. The device of claim 1, wherein the common transparent contact comprises a negatively doped GaN layer covering the first end of the GaN nanopillar array.

3. The device of claim 1 or 2, wherein the GaN nanopillar array is coated with an insulating material and the insulating material is coated with a reflective material to help direct light in the nanopillars to the exit window.

4. A device according to claim 1, 2 or 3, wherein the gap filling material comprises a light absorbing material.

5. The device of any one of claims 1 to 4, wherein the GaN nanopillar array comprises a set of subpixels having different width dimensions and emitting different colors of light.

6. The device of any one of claims 1 to 5, wherein the light emitting region of the nanopillar is in a polar c-plane or a semi-polar plane to emit light directed to the first and second ends.

7. The device of any one of claims 1 to 6, wherein the metal coating comprises nickel and gold, the nickel and gold Jing Re treated to bond with the second ends of the GaN nanopillar array.

8. The device of claim 7, wherein the metal coating is about 6nm thick and comprises about equal amounts of nickel and gold.

9. The device of any one of claims 1 to 8, wherein the array of reflective conductive contacts is arranged in an array of pixels and the driver semiconductor substrate is configured to provide an image display device.

10. The device of claim 9, wherein the array of gallium nitride (GaN) nanopillars is arranged in a subpixel group for providing a color image display device.

11. The device of claim 10, wherein the number of subpixel groups is four or more.

12. The device of any one of claims 1 to 8, wherein the reflective conductive contact array is arranged to drive groups of the gallium nitride (GaN) nanopillar arrays to provide different colors, and the driver semiconductor substrate is configured to provide different voltages to the groups for providing a variable color lighting device.

13. A method of fabricating a monolithic nanopillar light emitting device, the method comprising:

applying a metal coating on the p-doped ends of an array of gallium nitride (GaN) nanopillars, the metal coating having a thickness sufficient to bond with the p-doped ends of the array of GaN nanopillars while being thin enough to have low absorption of light emitted from the light emitting regions of the GaN nanopillars;

one of the following:

coating each nanopillar of the GaN nanopillar array with an insulating material, wherein the insulating material covers sidewall surfaces over an entire length of each nanopillar extending over an n-doped end, a light emitting region, and the p-doped end of each GaN nanopillar; and

coating the insulating material of each nanopillar of the GaN nanopillar array with a reflective material to help direct light in the nanopillar to an exit window; and

coating each nanopillar of the GaN nanopillar array with a dielectric reflective material covering a sidewall surface over an entire length of each nanopillar extending over an n-doped end, a light emitting region, and the p-doped end of each GaN nanopillar to help direct light in the nanopillar to an exit window;

An array of reflective conductive contacts is applied, each reflective conductive contact covering the metal coating of a number of the GaN nanopillars representing a pixel or subpixel for reflecting the light to the exit window, wherein the metal coating provides a reduced resistance between the p-doped GaN of the nanopillars and the reflective conductive contacts.

14. The method of claim 13, comprising:

the GaN nanopillar array is grown on a buffer layer of n-type doped GaN capable of providing a common contact and the exit window.

15. The method of claim 13 or 14, further comprising:

a driver semiconductor substrate having surface contacts is attached, the surface contacts being connected to the reflective conductive contact array.

16. The method of claim 13, 14 or 15, comprising:

coating the GaN nanopillar array with an insulating material; and

the insulating material is coated with a reflective material to help direct light in the nanopillars to the exit window.

17. The method of claim 13, 14 or 15, comprising:

the GaN nanopillar array is coated with a dielectric reflective material.

18. The method according to any one of claims 13 to 17, comprising:

And filling the gap space between the GaN nano-pillar arrays with a gap filling material.

19. The method of claim 18, wherein the filler material is a light absorbing material.

20. The method of any of claims 13-19, wherein the GaN nanopillar array comprises a set of subpixels having different width dimensions and emitting different colors of light.

21. The method of any one of claims 13 to 20, wherein the light emitting region of the nanopillar is in a polar c-plane or a semi-polar plane to emit light directed to the first and second ends.

22. The method of any one of claims 13 to 21, wherein the metal coating comprises nickel and gold, the nickel being deposited first, the gold being deposited on the nickel and heat treated to bond to p-doped ends of the GaN nanopillar array.

23. The method of claim 22, wherein the metal coating is about 6nm thick and comprises about equal amounts of nickel and gold.